1. Field of the Invention
The present invention relates to a process for preparing a calcium silicate shaped product, more particularly, it relates to a process for preparing a calcium silicate shaped product which is suitable as a lagging product or a heat insulator.
2. Description of the Prior Arts
It has been known to prepare calcium silicate products by the following processes.
(1) A slurry is prepared by dispersing and mixing a siliceous source and a calcareous source and optionally inorganic materials such as clay, asbestos with water and the slurry is poured into a mold and cured in an autoclave (steam curing) and the cured product is taken out from the mold and dried.
(2) The slurry prepared by the process (1) is heated at 80.degree. to 100.degree. C. and is poured into a mold and shaped with a press filter molding and the product is taken out from the mold and cured in an autoclave and dried.
(3) The slurry prepared by the process (1) is heated under higher pressure with stirring to crystallize and the resulting slurry containing crystalline calcium silicate hydrate is poured into a mold and the product is shaped with a press filter molding and taken out from the mold and dried.
When a calcium silicate product is used as a lagging product or a heat insulator, it is usually necessary to have high porosity that is, low bulk density in order to obtain a product having low thermal conductivity. However in the conventional processes (1) and (2), it has been difficult to obtain a product having low bulk density such as less than 0.2 g/cm.sup.3 especially less than 0l.3 g/cm.sup.3 e.g. about 0.1 g/cm.sup.3. In the conventionl process (3), it has been possible to obtain a product having low bulk density however, the mechanical strength has been remarkably low, disadvantageously.
The inventors have studied this in order to overcome the difficulties.